docs: def _select_theory(theories):
          """Return the most likely spacing convention given different options.
  
          Given a dictionary of convention options as keys and their occurrence
          as values, return the convention that occurs the most, or ``None`` if
          there is no clear preferred style.
          """
          if theories:
              values = tuple(theories.values())
              best = max(values)
              confidence = float(best) / sum(values)
              if confidence > 0.5:
                  return tuple(theories.keys())[values.index(best)]